Polarizing Filters

Try this if you're not familiar with the effect:
Position two polarizing filters with their polarizing axis' at right angles to one another so they block the light passing through them? Okay, now, keeping the positions of those two, position a third polarizing filter between them with its axis at 45 degrees to the first two.
Why does light now pass through all three filters?

This is just a guess, but here's my hypothesis:
When the light passes through the first filter, the vibration in one plane is blocked. When you place another one at 45 degrees, it polarizes the light so that it now vibrates with a 45-degree rotation relative to the first plane that it was restricted to.